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Nitrous oxide emissions from cool-season pastures under managed grazing

High stocking densities on grazed pastures may promote nitrous oxide (N₂O) loss from soil to the atmosphere. However, studies of N₂O fluxes in cool-season pastures of North America are lacking. We performed two experiments in which measured N₂O fluxes were bootstrapped with re-sampling (n = 100, wit...

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Published in:Nutrient cycling in agroecosystems 2015-04, Vol.101 (3), p.365-376
Main Authors: Jackson, Randall D, Oates, Lawrence G, Schacht, Walter H, Klopfenstein, Terry J, Undersander, Daniel J, Greenquist, Matthew A, Bell, Michael M, Gratton, Claudio
Format: Article
Language:English
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Summary:High stocking densities on grazed pastures may promote nitrous oxide (N₂O) loss from soil to the atmosphere. However, studies of N₂O fluxes in cool-season pastures of North America are lacking. We performed two experiments in which measured N₂O fluxes were bootstrapped with re-sampling (n = 100, with 10,000 iterations), which allowed us to generate an empirical distribution of mean fluxes to understand how pasture management strategies might affect N₂O emissions. In Experiment 1, N₂O fluxes were estimated in southern Wisconsin pastures under rotational grazing, continuous grazing, haymaking, and no agronomic production. Nitrous oxide fluxes were significantly positive under rotational grazing at our research farm [21.6 (se = 10.3) μg m⁻² h⁻¹], but not significantly different than zero under the other three treatments or rotationally grazed paddocks across eight working farms. In Experiment 2, we measured N₂O fluxes in eastern Nebraska before, during, and after two rotational grazing events under two N-input treatments—inorganic N fertilizer and supplemented dried distillers grains—and an unfertilized control. Nitrous oxide fluxes were positive (20–100 μg m⁻² h⁻¹) in periods following rain, but otherwise not significantly different than zero. Post-grazing, N₂O emissions were lower from the control than fertilized or supplemented treatments. These experiments show cool-season pastures can be a source of N₂O to the atmosphere, but primarily following grazing events that coincide with significant precipitation. However, even though on-farm paddocks are in varying states of recovery from defoliation, farm scale emissions, although episodic, are likely to be positive in years with above average precipitation.
ISSN:1385-1314
1573-0867
DOI:10.1007/s10705-015-9685-6